It is often necessary to quickly obtain a sample of blood and perform an analysis of the blood sample. Preferably obtaining the blood is as painless as possible. One example in which there is a need for painlessly obtaining a sample of blood is in connection with a blood glucose monitoring system where a user must frequently use the system to monitor the user's blood glucose level.
One method of monitoring a person's blood glucose level is by portable handheld blood glucose testing device. The portable nature of these devices enables the user to conveniently test his blood glucose levels wherever the user may be. To check the blood glucose level, a drop of blood is obtained from him, for example, from the fingertip using a separate lancing device. The lancing device contains a lance or lancet to puncture the skin. Once the requisite amount of blood is produced on the fingertip, the blood is harvested using the blood glucose-testing device. The blood is drawn inside the testing device, which then determines the concentration of glucose in the blood. The results of the test are communicated to the user by a display on the testing device.
Many prior art lancing devices use a spring directly coupled to the lance to move the lance to its penetration depth. The lance is drawn back to compress the spring. When released, the spring extends, thus forwardly propelling the lance to its penetration depth. More detail concerning lancing devices is set forth in U.S. Pat. No. 6,152,942, which is commonly assigned and incorporated herein by reference in its entirety. One problem associated with other prior lancing devices is that the penetration depth of the lance is dependent on a spring constant, which is a measure of the spring stiffness. The mechanical quality of the spring, including the stiffness, tend to vary, and in particular degrade, over time with use. Accordingly, over time, the penetration depth of prior art lances may vary. When the penetration depth of the lance lessens over time, the lance may not produce a laceration deep enough to draw the requisite volume of blood necessary for blood glucose analysis. Insufficient lancing can result in erroneous analysis if the user does not recognize that the lancing has not produced the requisite volume of blood for analysis. And if the user does recognize an insufficient lancing has incurred the user must re-lance resulting in another laceration in the user's skin and more pain. The user may eventually have to replace the lance, or the entire device because the accuracy and consistency of the laceration has degraded.
Another related problem associated with many prior art lancing devices is that when the spring forwardly advances the lance to its penetration depth, the spring extends past its static length. The spring then retracts the lance. But due to the oscillary nature of the spring, the lance is retracted past its static retraction position. If the lance continues to oscillate in this manner, it may repeatedly enter the laceration and penetrate the user's skin several times. With each actuation of such an oscillating lance, the user's skin is lanced several times which results in a larger laceration. A larger laceration in the user's skin translates into more pain for the user and a longer time for the laceration to heal.
Other problems associated with prior art lancing device include vibration and chatter of the lance during the lancing process. The vibration and chatter result in uncontrolled movement of the lance. Such uncontrolled movement may result in larger as well as more jagged lacerations. Another detrimental result is inaccurate punctures in the skin, with respect to both location and depth of the puncture.
Accordingly there is a need for continued improvement in lancing devices and glucose monitoring systems generally.